Pre-filled syringes that are filled with a selected dosage of a medication are well known injection devices for administering the medication to a patient. Safety devices for covering a needle of a pre-filled syringe before and after use are also well known. Typically, these devices comprise a needle shield that is either manually moved or moved by the action of a relaxing spring to surround the needle.
A different type of safety devices known in the state of the art solves the object of providing needle safety by arranging the pre-filled syringe movable relative to a body, whereas the pre-filled syringe is retracted into the body after the injection.
Document WO 2006/111864 A1 describes an injection assisting device suitable for housing a syringe. The injection assistance device comprises a hollow sleeve and a sleeve tube that are able to move with respect to each other. The sleeve tube is coupled to a piston plunger. The piston plunger may be depressed into the syringe and the medicament disposed therein may be expelled by manually translating the sleeve tube with respect to the hollow sleeve. The sleeve tube further comprises a substantially planar side wall with a cam formed thereinto. A peg is coupled to the hollow sleeve by a flexible tab. The peg moves within and along the cam when the hollow sleeve and the sleeve tube are axially translated relative to each other to control the movement of the hollow sleeve. After the injection is completed, the interaction of the peg and the cam prevents any further axial displacement of the sleeve tube and the hollow sleeve so as to lock the hollow sleeve into a position wherein a needle of the syringe is covered.
The U.S. Pat. No. 5,279,579 discloses a sleeve cover that is slidably engaged to a hub of an injection needle assembly or syringe. The sleeve cover has a longitudinal groove disposed in the side wall that is adapted to guide a pin protruding radially from the hub between protective and unprotective positions.
Document US 2005/0113750 A1 a safety needle for use with a syringe. The safety needle has a cylindrical casing in which a sleeve is slidably mounted. A locking mechanism prevents re-exposure of the needle. The locking mechanism includes a plurality of fingers connected to the sleeve. At least one of the fingers has a projection that travels along a track system disposed in the inner surface of the casing when the sleeve is translated with respect to the casing.